GB/T 3398.2-2008Plastics -- Determination of hardness -- Part 2: Rockwell hardness (English PDF)

Foreword

GB/T 3398 "Determination of Hardness of Plastics" is divided into two parts.

--- Part 1: Ball indentation method;

--- Part 2: Rockwell hardness.

This part is the second part of GB/T 3398, which is equivalent to ISO 2039-2:1987 "Plastic --- Determination of hardness --- Part 2.

Rockwell Hardness (English version).

For ease of use, this section has made the following editorial changes.

a) Change the word "this International Standard" to "this standard" or "GB/T 3398", change "this part of ISO 2039" to "GB/T 3398 "this section" or "this section";

b) Delete the preamble of ISO 2039-2:1987;

c) Added the preamble of this part of the national standard;

d) Replace the international standards listed in the "Normative References" chapter with the corresponding Chinese national standards that are equivalent to adopting this document;

e) Replace the decimal point symbol "," in the international standard with the decimal point symbol "." in my country;

f) Change the Rockwell-alpha hardness "Ralpha" in the formula in Appendix A of this international standard to "HRalpha".

This part replaces GB/T 9342-1988 "Plastics Rockwell Hardness Test Method".

Compared with GB/T 9342-1988, the main changes in this part are as follows.

--- "Not applicable to the determination of plastic films and foams" has been canceled in the scope;

--- cancel the definition;

--- Increased principle;

--- Canceled the requirements for racks, steel balls and timing devices;

--- Added 3 referenced standards and removed 1 referenced standard.

Appendix A of this section is a normative appendix.

This part is proposed by China Petroleum and Chemical Industry Association.

This part is under the jurisdiction of the National Plastics Standardization Technical Committee (SAC/TC15).

1 Scope

1.1 This part of GB/T 3398 specifies the method for determining the indentation hardness of plastics with Rockwell hardness tester M, L and R scales.

1.2 The Rockwell hardness value is directly related to the indentation hardness of the plastic material; the higher the Rockwell hardness value, the harder the material. When using this method, since Partial overlap between Rockwell hardness scales, the same material may get different Rockwell hardness values on two different scales, and these two values are technically both are likely to be correct.

1.3 For materials with high creep and high elasticity, the time factor of main load and initial load has a great influence on the test results.

1.4 Appendix A specifies another method for determining the Rockwell hardness using the Rockwell-alpha hardness scale, which shows that the Rockwell-alpha scale and GB/T 3398.1 The relationship between hardness measurement.

2 Normative references

The terms in the following documents become the terms of this part through the reference of this part of GB/T 3398.All dated citations documents, all subsequent amendments (excluding errata content) or revisions do not apply to this section, however, it is encouraged to reach the parties to the agreement research the availability of the latest versions of these documents. For undated reference documents, the latest version applies to this part.

3 Principles

3.1 The method for determining the hardness in this part is to apply a constant initial load on the steel ball above the test material within the specified loading time.

load, then apply the main load, and then return to the same initial load. The measurement result is determined by subtracting the total depth of indentation after removing the main load.

The elastic recovery in the space and the indentation depth caused by the initial load. Rockwell hardness is increased by the load on the indenter from the specified initial load to the main load, Then return to the same initial load to obtain the net increment of indentation depth.

3.2 Each division of the Rockwell hardness scale represents the vertical movement of the indenter by 0.002mm. In fact, the Rockwell hardness value is obtained by formula (1).

4 Instruments

4.1 The instrument is a standard Rockwell hardness tester, which mainly consists of the following components.

a) a rigid frame with an adjustable table, with a flat plate with a diameter of at least 50 mm for placing the specimen;

b) Indenters with connectors;

c) Means for applying a suitable load to the indenter without impact.

4.2 The indenter is a hard polished steel ball that can freely roll in the bushing. The steel ball should not be deformed during the test and should not be damaged after the test.

The diameter of the indenter depends on the Rockwell hardness scale used (see 4.5).

4.3 The indenter is equipped with a dial gauge or other suitable device to measure the indentation depth of the indenter, accurate to 0.001mm. Dial gauge is best to press Rockwell hardness scale scale number (but not necessary), (each division value of Rockwell scale is 0.002mm). When the instrument is marked directly, the thousandth There are usually black and red scales on the scale, and the latter has automatically calculated the constant 130 of the Rockwell hardness of the M, L and R scales (see 3.2). as long as it is accurate the accuracy is not lower than the dial indicator, and other means of measurement and data display can also be used.

4.4 4.5 lists the loads corresponding to the M, L and R scales. The initial load in all cases was 98.07N. Rockwell Hardness Tester the workbench where the sample is placed is raised through the screw rod until the sample contacts the indenter to apply the initial load. In this case, the dial indicator has a the indicator point showing that the initial load has been applied. Before operating the hardness tester, the manufacturer's instrument manual should be consulted. Adjusting the loading speed is extremely important.

Adjust the shock absorber of the Rockwell hardness tester so that the operating handle can complete within 4s~5s when there is no sample on the instrument or no load on the anvil.

As a result, the main load used for this operation should be 980.7N.

4.5 The main load, initial load and indenter diameter of the Rockwell scale are shown in Table 1.

4.6 The instrument should be installed on a level, non-vibrating steel base. If the pedestal of the instrument cannot be protected from vibrations (e.g. on its near other testing machines), the Rockwell hardness tester can also be installed on a metal plate with a sponge rubber backing at least 25mm thick, or other materials that can have a on a pedestal with effective vibration damping.

4.7 Regularly use standard hardness blocks of known Rockwell hardness metals (cast iron, aluminum-magnesium alloy, bearing materials), and use the Rockwell E scale to calibrate the instrument.

In this way, errors caused by failure of the loading device or deformation of the frame can be found, and these errors should be corrected before the instrument is used. when when the instrument specifies the test method of R, L or M, it can often be assisted by the standard hardness block used in the corresponding test method of R, L or M.

check.

5 Samples

5.1 The standard sample is a flat plate with a thickness of at least 6mm. Its area should meet the requirements of 7.4.The specimen does not have to be square. After the test There should be no indentation of the indenter on the support surface.

5.2 When the sample with the minimum thickness specified in 5.1 cannot be obtained, it can be stacked with thinner samples of the same thickness, and the surface of each sample is required the surfaces shall be in close contact and shall not be separated by surface imperfections of any kind (for example, dent marks or burrs from sawing).

5.3 All indentations should be on the same surface of the sample.

5.4 Only one sample is needed to measure the Rockwell hardness. For isotropic materials, each sample should be measured at least 5 times.

5.5 When the test material is anisotropic, the relationship between the direction of the indentation and the axis of anisotropy shall be specified. When more than one direction needs to be measured when the hardness value is higher, enough samples should be prepared so that at least 5 Rockwell hardness values can be determined in each direction.

6 State regulation

Before the test, the sample should be in the environment specified in the standard related to the test material or in an environment specified in GB/T 2918-1998.

state adjustment in the environment.

7 Operation steps

7.1 Unless otherwise specified, the test shall be carried out in the same standard environment as the condition conditioning.

7.2 Check whether the main load, initial load and indenter diameter are consistent with the Rockwell scale used (see 4.5). The pressure head cannot be correct due to manual adjustment seated in the housing, the first reading after replacing the ball must be discarded. The full pressure of the main load is required to seat the ram on the shaft in the seat.

Note 1.See 4.7 for periodic calibration of the instrument.

7.3 Put the sample on the workbench. Check the surface of the sample and the indenter for dust, dirt, lubricating oil and rust, and check the surface of the sample is it perpendicular to the direction of the applied load.

Apply initial load and adjust dial indicator to zero. Apply the main load (4.4) within 10s after applying the initial load. After applying the main load the main load is removed at 15+10s. The instrument should be operated smoothly. Read the reading on the dial indicator 15 seconds after the main load is removed, and it is accurate to the minute of the scale.

degree value.

Note 2.If the instrument is directly graduated according to the Rockwell hardness value, it is suitable to operate according to the following method. count the number of points that the pointer passes through the zero point on the red scale after the main load is applied.

Subtract the number of times obtained from the number of times the pointer passes through zero after the main load is removed. If the difference is zero, the hardness value is the scale reading plus 100.

If the difference is 1, the hardness value is the scale reading; if the difference is 2, the hardness value is the scale reading minus 100.In case of doubt, consult the factory instrument manual.

7.4 Make 5 measurements on the same surface of the sample. Each measurement point should be more than 10mm away from the edge of the sample, and the distance between any two measurement points not less than 10mm.

7.5 Theoretically, the Rockwell hardness value should be between 50 and 115; the value beyond this range is inaccurate, and the adjacent scale should be used to retest Determination.

Note 3.If a scale with a lower hardness value than the R scale is required, the Rockwell hardness test is not suitable, and the material should be in accordance with the provisions of GB/T 2411-2008 method to test.

8 Results show

8.1 The Rockwell hardness value is represented by a number prefixed with a scale letter.

8.2 If the Rockwell hardness tester is a direct hardness scale, record the Rockwell hardness value after each test (see note 2 in 7.3).

8.3 If necessary, calculate the Rockwell hardness value (see 3.2).

8.4 When necessary, estimate the standard deviation according to formula (2).

9 Precision

The precision of this test method is unknown because interlaboratory test data are not yet available. If the above data is obtained, in the next revision Include a statement of precision.

10 Test report

The test report should include the following.

a) Indicate the adoption of this part of GB/T 3398;

b) complete identification statement of the test material;

c) The description, size and method of sample preparation of the relevant sample;

d) State adjustment and test environment conditions;

e) number of tests;

f) Rockwell hardness scale (M, L or R);

g) Rockwell hardness value, single value and average value;

h) Standard deviation of the results, if required.